Construction of an LAN (Local Area Network) by connecting a plurality of computers provides sharing information such as files and data, sharing peripheral devices such as a printer, and interchanging information such as forwarding electronic mail or data content.
Conventionally, the wired LAN connection with optical fibers, coaxial cables, or twist-pair cables was general. This case requires wiring constructions, which makes it difficult to simply construct a network and makes works for laying cables troublesome. Further, after the construction of a LAN, the length of the cable connected to a device limits the movable range.
Then, wireless LANs draw attention as a system releasing users from the LAN wiring in the wired system. According to the wireless LAN, at operation spaces of offices or the like, most of all part of wiring cables can be omitted, so that communication terminals such as personal computer (PC) can be moved relatively easily. Recently, the demands have remarkably increased with the advance in high speed in the wireless LAN system and lowering the cost. In particular, to construct a small scale of wireless network among a plurality of electronic devices existing around human beings to effect information communication, recently introducing a personal area network (PAN) has been studied. For example, different wireless communication systems are defined using frequency bands for which governmental licenses are not required such as the 2.4 GHz band, the 5 GHz, and the like.
In a communication system constructed of a plurality of terminals, it is known that an access control is necessary to avoid collisions of communication between terminals. The access control in the wireless network includes the channel occupied system such as the FDMA (Frequency Division Multiple Access: Frequency Division Multiple Access), the TDMA (Time Division Multiple Access: Time Division Multiple), the CDMA (Code Division Multiple Access: Code Division Multiple Access), or the channel shared system such as the ALOHA or the CSMA (Carrier Sense Multiple Access: Carrier Sense Multiple Access).
For the packet communication having a high burst characteristic due to random communication demands, the channel shared systems, in which a plurality of terminals share the same frequency channel, are frequently adopted. In this channel shared system, communication requests randomly done from the terminals may cause collisions of signals from a plurality of terminal stations (i.e., transmission at the same time interval). Since the collision will decrease the service quality in communication, as a method for avoiding this, the CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance: Carrier Sense Multiple Access/Collision Avoidance) system is widely adopted.
Further, it is known that “Ad Hoc communication” freely constructing a network within communicable regions of respective wireless communication apparatuses, without proving a specific base station or a control station, is suitable for constructing a small scale of personal area network (PAN). In the Ad Hoc communication system, an access control is also adopted to detect whether own transmission type of transmission does not collide.
Further, in the wireless communication system, a method of inserting a preamble having a known pattern at the top of the packet for synchronization among the communication apparatuses is generally adopted.
For example, a system for wireless communication in which information is superimposed on an extreme week impulse stream draws attention as a wireless communication system realizing a near field ultra high speed transmission and is expected to be actually used. The UWB transmission system includes two types, namely, the DS-UWB system in which a diffusion speed of the information signal of the DS is increased to the upper limit and the impulse-UWB system in which the information signal is formed with an impulse scream having an extremely short period at about hundreds picoseconds. Both systems provide high speed data transmissions by diffusion toward an ultra high frequency band, for example, from 3 GHz to 10 GHz to execute transmission and reception. The occupied bandwidth is that of a GHz-order such that the value obtained by dividing the occupied band width by its center frequency (for example, 1 GHz to 10 GHz) becomes about 1. This has an ultra wide band if it is compared with the band width generally used in the wireless LAN or the like using the so-called W-CDMA or cdma2000 system, SS (Spread Spectrum) or OFDM (Orthogonal Frequency Division Multiplexing) system.
Recently, in IEEE802.15.3, as an access control method for the ultra wide band communication, a data transmission method for a packet structure including a preamble is proposed.
Further, after the transmission of data from an information transmission source communication apparatus, when an information reception target communication apparatus side succeeds in data reception, as an automatic retransmission control method, a method of immediately returning reception confirmation information (immediate ACK) has been generally adopted. In this case, at the information transmission source communication apparatus side recognizes the completion of the data transmission when the immediate ACK can be received within a predetermined interval after the data transmission, but on the other hand, when the immediate ACK cannot be received within the predetermined interval, it recognizes the incompletion of the data transmission. In the case of the latter, a data retransmission process is activated.
Further, in the wireless communication system, as another method to improve a communication quality with avoiding collisions, the RTS/CTS method is given. In this case, before the transmission of the body of the information, the information transmission source communication apparatus transmits an RTS (Request to Send: transmission request). When the information reception target communication apparatus receives this RTS, and if the data reception is possible, a CTS (Clear to Send: confirmation notice) is returned as the response. Then, after establishment of connection between the apparatuses by interchanging the RTS/CTS information, the data transmission is executed.
Here, in the ultra wide band communication mentioned earlier, the communication is executed with extremely weak impulse streams, and thus, it has no specified frequency-like carrier. Thus, there is a problem that it is difficult that the access control method on the basis of the CSMA/CA using the reception electric field intensity information (RSSI) cannot be adopted as it is.
On the other hand, in the reception apparatus, a system can be considered which transmits an access control signal to inform the peripherals about its reception condition during the interval for which the signal directed to own station is received. In this case, the communication apparatus during non-communication state holds the use condition of the transmission path with a lead of the reception of the access control signal.
However, if the use of transmission is notified during communication state, the communication apparatus on the reception side is required to transmit and receive the data at the same time. Further, it is required to transmit the access control signal by using a signal of a different frequency band, changing the diffusion code, or selecting timings with which impulses do not overlap. This makes the control complicated.
Further, in such a wireless communication system as to hold the user of the transmission path on the basis of a preamble signal, if a retransmission control is automatically executed on the basis of presence and absence of return of a reception confirmation information (immediate ACK) within a predetermined interval, other communication apparatuses cannot be known about the start of retransmission as long as the preamble signal once added to the NACK information is not transmitted from the information reception target. Thus, loss of time is expected.
In addition, in the wireless communication system interchanging the RTS/CTS information, it is necessary to undergo a connection procedure between the information transmission source and the signal reception target before the data transmission. Thus, the adoption of a method using the preamble signal corresponding to a redundant time added before a signal will cause a problem that it takes for a long period to conduct the connection procedure.